The present invention relates to a water tapping point and a tap water network effectively impeding bacterial growth, in particular, legionella bacteria growth, in the water tapping point as well as in the water network.
One problem of known tapping points is that especially the hot water space and the mixing chamber constitute an environment for the growth of water-borne bacteria, especially the feared legionella bacteria that can increase in numbers up to 10,000-fold within 48 hours if the water temperature is about 35xc2x0 C. The legionella bacterium does circulate in water as a free-living organism, and is also a part of a very complex micro-environment that is found, for example, on the inside of water tanks, water pipes and mixers. The biofilm, which there consists of micro-organisms, becomes a thin layer of slime and is surprisingly resistant to influences such as biocides used specifically for the purposes of combating the growth of the bacteria. A biocide may effectively kill all free-living bacteria in the water, but the bacteria in the biofilm will often survive and start to multiply in the water as soon as the conditions allow it. This capability of xe2x80x9chidingxe2x80x9d makes certain bacteria e.g. legionella very difficult to effectively control. The problem is increasing, supposedly related to the more widespread use of modern apparatuses having spaces with stagnant water allowed to cool down or warm up to the hazardous temperature region of 25-50xc2x0 C. A typical example of such apparatus and a potential source of legionella bacteria being modem thermostatic mixers. Bacterial growth is considered to cease at temperatures above 50xc2x0 C.
Recent attempts to address this problem have included mixers where an operator can use a special tool to temporarily flush the mixer and the water supply system with scalding hot water for several minutes with the aim of killing the bacteria during a round of all the tapping points in a hospital or care establishment, for example. A computer-controlled automated system for the regular flushing of mixers with hot water has also been suggested. Further experience has shown sanitizing effects are achieved by continuously supplying the water with oxidising biocides such as chlorine, bromine or ozone. Flushing methods are taught in e.g. U.S. Pat. No. 6,027,572 and references therein. However, all such procedures imply a great deal of manual labor and consequently costs for the service operator in, for example, a hospital. In addition, the activities in the clinics will be disrupted.
Other attempts of addressing the bacteria problem is by purifying the water in, or close to, the tapping device. Methods and devices include adding ozone (U.S. Pat. No. 5,942,125), using multiple filters (U.S. Pat. No. 5,851,388), adding bactericidal agent through a pumping device (U.S. Pat. No. 5,709,546) and sterilization by UV radiation (U.S. Pat. No. 5,891,329). Although effective in certain applications e.g. in dental units, their complexity and need for maintenance make them less suitable for large-scale installation such as every tapping device in a hospital or an apartment building. Also the principle of purifying water at a late stage and not addressing the problem of the rapid growth of bacteria could be questioned.
In a recently granted U.S. Pat. No. 6,021,803, by the same applicant as in the present invention the problem of legionella bacteria is addressed by providing a tapping point including a mixer for hot and cold water, with a hot water and a cold water inlet, and a hot water and a cold water space. To impede the growth of especially legionella bacteria within the mixer it is suggested that the mixer additionally is provided with a hot water outlet from the hot water space of the mixer. The outlet is connected to a hot water return pipe and through an arrangement of valves the hot water is always kept under circulation. This will assure that the water will not cool down to the hazardous temperature region 25-50xc2x0 C. Thermally insulated return pipes for hot water are, in fact, often already installed in the water mains network of a building, whereby in such cases, the return pipes only need to be furnished with branches off to the respective tapping point. This will keep the installation and maintenance cost at a reasonable level. U.S. Pat. No. 6,021,803 is incorporated by reference herein.
Traditionally legionella and other bacteria have been considered to be a problem mainly in systems with heated water. Recently attention has been drawn also to the cold water systems. If the cold water is kept immovable for a long period it could heat up to the dangerous temperature region 25-50xc2x0 C., for example during a hot summer day. Another potential risk is that the cold water system is heated by the hot water system. For example in a common thermostatic mixer the cold water spaces can be heated through thermal conduction from the hot water parts. Similarly warming up through thermal conduction could occur if the hot and cold water pipes are poorly isolated and too close to each other. At temperatures below 18xc2x0 C. legionella growth is known to be very limited. To the best knowledge of the inventor no prior art tapping points are designed to limit the heat transfer between hot and cold parts.
In U.S. Pat. No. 6,021,803 it is suggested that the cold water is circulated in the same manner as the hot water. This would be an effective way of limiting the bacteria growth, but it would require a return system also for the cold water. In addition a cooling system would be needed in order to avoid continuously warming up the water. Return pipes for cold water do normally not exist in the mains, nor equipment for cooling the water. This system would in many cases be too complicated and expensive, especially if installed in existing buildings.
To summarize the requirements to keep legionella growth at minimum: The hot water should be hot at all times, and the cold water should be cold at all times and spaces with immovable water should be carefully avoided. To keep the investments and the maintenance cost at reasonable levels the system must not require a complete new backbone network of water mains or tapping points requiring frequent maintenance. None of the prior art fulfills these requirements.
In conventional tap water networks the water is, in certain spaces, allowed to warm up or cool down to temperature regions hazardous for bacterial growth. Known solutions for solving this problem are costly to install, or require frequent maintenance.
One object of the present invention is to overcome the drawbacks of the prior art by providing a tap water network that effectively impedes bacterial growth in all parts of the network.
Another object is to provide providing a tap water network that effectively impede bacterial growth at reasonable installation and maintenance costs.
In order to achieve the above-mentioned objects, according to the invention, a tapping point is provided that allows continuous circulation of hot water in its hot water parts and continuous circulation of cold water in its cold water parts.
The inventive tapping point gives the possibility to construct a water network with constant circulation of hot and cold water in all parts of the network. Any parts not suitable to circulate with hot or cold water are evacuated and ventilated.
A realization of the above-mentioned objects, according to one aspect of the invention, is a tapping point comprising a hot water inlet; a cold water inlet, a hot water space; a cold water space, a mixing chamber, a hot water outlet from the hot water space and a cold water outlet from the cold water space, providing a flow of hot return water from the hot water outlet and a flow of cold return water from the cold water outlet. An advantage with this arrangement is that the cold water always circulates and therefore remains cold in the cold water space and the warm water always circulates and therefore remains warm in the hot water space. This will effectively impede bacterial growth. In addition convenience is added for the user as cold and hot water will always be present when starting to use the tapping point.
The flow of return water from the hot water outlet and the flow of return water from the cold water outlet are combined into a common flow of return water. In doing so circulation of both the hot water and the cold water is achieved without the need of a separate cold water return network. The common flow of return water is thus arranged to flow in a common return water pipe.
According to one preferred embodiment of the invention the water tapping point comprises a hot water inlet; a cold water inlet, a hot water space, a cold water space, a mixing chamber; a hot water outlet from the hot water space and a cold water outlet from the cold water space. The hot water outlet from the hot water space and the cold water outlet from the cold water space are combined, by passage means, into a common return water outlet, the latter being adapted for connection to a common return water pipe.
According to another embodiment of the invention the hot water outlet and the cold water outlet are provided with adjustment valves to control the flow and temperature of the return water. The adjustment valves are typically set once so that the common flow of return water gives a desired flow at a desired temperature which preferably is above 50xc2x0 C.
According to yet another embodiment of the invention the mixing chamber is provided with a pressure sensitive valve, said valve arranged to open when the tapping point is not in use in order to drain and ventilate the mixing chamber and preferably also any equipment connected to the mixer chamber such as a shower hose, for example.